A shuttle device utilizing a long span screw and nut drive have been used to transmit heavy torque and thrust loads at relatively high speeds. One such device is shown in U.S. Pat. No. 3,670,583 in the name of John C. Leming, which includes a nonrotatable coactive nut operatively mounted on a rotary screw and adapted to travel freely linearly along the screw.
The problem with conventional lead screws and nut drive assemblies is that the nut threads have to be machined to match the threads of a lead screw. At high speeds, the nut drive and lead screw may vibrate due to the tolerance difference between the lead screw and nut drive threads. Also, misalignment of the nut drive and lead screw may occur due to the machining tolerances on the threads of the nut drive. Further, large amounts of power are required to drive various loads due to the large amount of pitch in a single lead screw.
One approach to correcting this problem has been to inject the nut with an epoxy material called Moglice. The Moglice material has special fillers that allow it to have high strength, lubricity, wearability, without the normal brittleness associated with epoxy. The nut thread form is injected into the screw directly as denoted in the Wedin Corporation publication "Diamant Moglice".
The problem with this approach is that the application of Moglice to a single thread lead screw will not permit high helix with high loads for high speed transfer. Further, a single thread lead screw has a helix ratio of one to one (1" lead for each 1" diameter) which requires the screw to operate at a very high RPM near the critical speed of the screw.